Palaeokarst, in the form of large, uncollapsed cave systems, is described from the Proterozoic of Kronprins Christian Land, eastern North Greenland. The endokarst, of entirely meteoric origin, is developed in dolostones of the Fyns Sø Formation (Hagen Fjord Group, Riphean). At one locality, Hjørnegletscher, shallow, sub-horizontal phreatic conduits are present below an unconformity surface and are infilled by the overlying Ediacaran Kap Holbæk Formation. In Sæfaxi Elv, the unconformity is overlain by the Wandel Valley Formation, an Early Ordovician carbonate sequence that is widely transgressive over northeastern Greenland. Vertical vadose fissures extend down towards the phreas, but the cave systems are again filled by Kap Holbæk Formation sediments. At Hjørnegletscher, channels up to 40 m wide incise the phreatic system, pointing to relative base-level lowering before, or during, deposition of the Kap Holbaek Formation.
Recognition of a depositional hiatus between the Fyns S0 and Kap Holbaek formations, in what was previously thought to be a continuous Vendian Hagen Fjord sequence, has implications for regional correlation and tectonics. The unconformity could represent most of Vendian time, accounting for the absence, in this area, of glaciogenic sedimentary rocks in the Hagen Fjord Group. This permits correlation of the Fyns SøFormation with other end-Riphean transgressive carbonate sequences developed in East Greenland, Svalbard and perhaps Scotland, that represent the culmination of a major pre-Iapetan rift-sag cycle.
Secondly, recognition of the scale of the sub-Wandel Valley unconformity points to regional uplift and tilting of northeastern Greenland in mid-Cambrian to earliest Ordovician time. This must represent a phase of renewed extension of the Iapetus passive margin that is unique to this corner of Laurentia, not terrane collision as previously suggested.
